A centrifugal compressor causes a working fluid to flow inside an impeller that rotates and compresses the working fluid using centrifugal force generated when the impeller rotates. As a centrifugal compressor, a multistage centrifugal compressor including a plurality of impellers and thus gradually compressing a working fluid and a geared compressor in which impellers are attached to ends of a plurality of pinion shafts are known.
As a structure including such a centrifugal compressor, for example, a compressor unit in which three centrifugal compressors are combined through gears is described in Patent Literature 1. The centrifugal compressor of the compressor unit described in Patent Literature 1 includes a flow path width-adjusting unit for adjusting a flow path width of an annular flow path connected to a scroll flow path. The flow path width-adjusting unit includes a disk plate fixed to a casing by a bolt and a shim for adjusting a protruding amount of the disk plate in the annular flow path. In the flow path width-adjusting unit, when the thickness of the shim is selected, a protruding amount of the disk plate with respect to the annular flow path is regulated and thus the flow path width is adjusted.